An airbag module is accommodated within the hub area of the steering wheel of almost every modern motor vehicle. The module has a housing, an inflation device—mostly in the form of a gas generator—and an airbag. The airbag is folded inside the housing and is spanned by a cover element which closes the housing. The cover element often also serves as the operating surface for the horn. In this case, the cover element can be pressed down against the steering wheel against the force of at least one spring element. Two basic designs are known of this type of system.
On the one hand, it is possible to connect the housing with the steering wheel in a fixed fashion and to arrange the cover element on the housing or the steering wheel so as to be moveable in axial direction.
Furthermore, it is possible to arrange the entire module, in other words the subassembly consisting of housing, gas generator, airbag and cover element, on the steering wheel so as to be moveable in axial direction. Such a design is known, for example, from patent application DE 196 25 722 A1. In that reference, compression springs are provided between the housing floor and the steering wheel, which push the housing away in the axial direction (related to the steering column). Positioning means which function in the axial direction are present, which limit the movement caused by the springs and define the axial position of the airbag module in the absence of forces from the outside. This means that—with the exception of when the horn is being operated—axial force is permanently transmitted between the airbag module and the steering wheel.
In addition to the requirement for a very high level of functional reliability, the requirement that the positioning of the airbag module in the steering wheel should be very precise for aesthetic reasons is playing an increasingly important role.